This came to me last week, a Walther LP2 in quite good condition. But as with all of these pistols that have not been rebuilt, the main seal had perished. I didn't so much as remove the old seal but more scrape it off!In this first picture the piston is attached to the cocking mechanism and the seal is still attached.

All I did was show it a scraping tool:

And here we are again, back at the Taig Lathe. The Soft Jaws are just the ticket for this. I am not yet sure exactly how I am going to approach this yet. I don't have a piece of urathene of a suitable size or hardness to make a new seal and even if I did I am not sure that is the right approach. I think machining a couple of grooves and using 'O' rings is the best and oft used solution but because the piston has the seal groove so close to the top a new crown on the piston and then 'O' rings is is probably a better solution. I will make further measurements tomorrow and decide then. The other observation is that the piston has suffered galling around the skirt and although I have absolutely not a jot of proof I would guess at some point a well meaning person probably used silicone grease as a lubricant and this is not up to the job. By all means, a slight smear of silicone grease on an 'O' ring as it rides against metal is good but silicone will not protect metal against metal, especially if those two metals are aluminium.

graham.I’m going off to go find myself. If I’m not back by the time I return, keep me here.

Before you do any alterations to that piston, check the JKI website - they have reproduction seals to fit those pistons, at a decent price.I have used them on LP3s that I have repaired and they fit and work as well as the OEM seals.

Prior to my learning of these reproductions from JKI, I used to machine the LP3 pistons to accept a Diana 24 piston seal.

Last edited by Leonardj on Sat Dec 21, 2013 9:53 pm, edited 1 time in total.

This is how I go about resealing the LP2 pistons, which had the seal molded into the piston head.The old seal is machined out of the piston, and then a new seal is made up from 90 DU urethane, and fastened to the piston. Works great.

I had explored the possibility of just cutting o-ring grooves in the LP3 pistons, but the pistons would have to have some major modification to use the o-rings - which is why I opted for the Diana 24 piston seal, which just required minimal modification to the piston.

If you cut the o-ring grooves far enough back from the face of the piston to avoid the original seal groove, you will loose a lot of compression with that extra headspace. Thus, you would have to machine the original piston to accept a sleeve that could be pressed into place, and be of appropriate diameter to allow the o-ring grooves to be cut without cutting through the sleeve.

For someone that does not have the resources to make the noted modifications to the original, or to make up their own seals, that eBay o-ringed piston kit is the only way to go - especially when dealing with the LP2 style pistons.

Well actually Leonard, what I had thought of doing was just to simply machine the piston crown down a couple of mm and recess it and then make up a piston "button". We used to do this regularly with the two stroke racing engines as you could significantly alter the geometry of the piston quite quickly and simply. We even tried making the Buttons out of Ceramic and that was twenty five years ago Most people think some of these more exotic materials are a new invention when in fact they have been around forever. It is quite simply that modern manufacturing techniques have reduced the cost and made these materials more available to the public, that and the Internet which enables you to actually find these things. I was looking for some PEEK the other day as I thought it would be ideal for something I was doing, then I saw the price That is obviously one material that has not come down in cost. Ninety pounds for a twelve inch length of bar stock. I used Delrin instead

graham.I’m going off to go find myself. If I’m not back by the time I return, keep me here.